1. Field of the Invention
The present invention relates to heating devices and more particularly to annular heaters adapted to apply heat to large cylindrical objects.
2. Description of the Prior Art
The use of plastic film around various wooden objects exposed to environmental deterioration has been known in the past. Typically such plastic film is applied around the exterior of objects like pilings or posts by wrapping the post with the plastic film and then fastening the film edges to the post. This manner of attachment, while providing some shielding to the post, is generally loose, particularly after a protracted term of exposure where the normal plastic flows in the film tend to enlarge the dimensions thereof, allowing for progressively larger gaps between the film and the protected post. In applications like marine pilings or harbor pilings, opaque plastic films are usually desired both to limit the sunlight and to limit the amount of oxygenated water flow between the film and the piling. The latter function in particular has been heretofore a source of problems particularly when compounded by the above-mentioned plastic deformation of the film with age. Furthermore the necessary use of fasteners directly attaching the film edges to the post results in stress concentrations should any stretching occur during the installation. One feature of polyethelene film in particular which, while known in the art, has not been successfully applied to piling shields or post shields, is the heat shrinking feature thereof. Generally, polyethelene insulation tubes have been used in electrical applications with particular success. Such insulation tubes, by virtue of their size, do not require any particular techniques of heat distribution during shrinking since generally the size of the article itself is much smaller than the normal variances in the heat source. When applied to large objects even heat distribution is far more difficult to achieve particularly when compounded with the manipulative difficulty of large objects.